Milwaukee battery M18 B4 4.0 Ah

Provides up to 2x longer run time, up to 20% more power and up to 2x longer battery life than other lithium-ion technologies and/or previous MILWAUKEE® battery technology (results depend on tool and application)
Battery REDLITHIUM™ protection with REDLINK™ digital overload protection to prevent the user from damaging their cordless tool in abusive situations.
Individual cell monitoring – ensures optimal charge and discharge for maximum battery life
Battery durable metal frame construction and shock-dampening separators prevent malfunction due to excessive vibration or drops.
Corresponding protection system directs water away from electronics and battery
Can be used in extreme temperatures down to -20 °C without affecting run time or battery life
The charge level indicator on the battery helps to use the battery with maximum efficiency